1. Field of the Invention
This invention relates to the charging of furnaces and particularly shaft furnaces. More specifically, the present invention is directed to a metering device which, in addition to enabling control of the flow of charge material being directed onto the hearth of a blast furnace, also permits the weight or volume of the charge to be accurately measured whereby the measured quantity may thereafter be employed to position the material flow control device. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use with a blast furnace. The construction of modern high production blast furnaces has imposed new and more stringent demands on the charging apparatus due in part to the increased internal pressures employed within the furnace and the increased dimensions of the hearth within the furnace over which the charge must be uniformly distributed. In order to optimize furnace operation; i.e., to obtain the greatest possible pig iron production in a large high pressure furnace; it is necessary to be able to measure and exercise control over all of the operating processes both in and on the furnace. Control of the of the charge of ore on the furnace hearth is a matter of primary importance because the profile of the charge provides the basis for the control of further operating processes within the furnace.
Among the problems which must be overcome in order to obtain the desired uniform operation of a blast furnace are those associated with the gassing of the charge material and the control of the distribution of the charge. A degree of success in avoiding disturbances to furnace operation by non-uniform gassing has been achieved through the expedient of pretreatment of all of the charge materials by grinding and screening to obtain a narrow grain size range and by sintering or pelletizing the material to achieve a charge which is as granular as possible. However, even with the uniform grain size the requisite high pressure at the furnace throat can not be maintained without also taking into consideration the profile of the charge. In fact, it has been found that the importance of charge distribution control is directly related to the degree of classification of the charge material. Restated, experience has shown that efforts to perform the charging process in such a way that the desired furnace operating parameters are not jeopardized must increase as the uniformity of the charge material increases.
The conventional furnace charging units of the prior art included a lower bell-type distributor. Furnace charging was accomplished by first loading the bell-type distributor and thereafter lowering the distributor into the furnace. These bell-type distributor charging devices inherently could not achieve a uniform distribution of the charge over the complete charging plane. That is, efforts previously made to supply bell-type distributors with charge material in a uniform manner over their periphery have not prevented the formation of a hollow cone below the distributors. In other words, the well known characteristic M-curve of the charge surface can not be avoided by the uniform distribution of the charge on the periphery of a lower bell-type distributor. The use of adjustable throat armors can only partially alleviate the considerable disadvantage of non-uniform charge distribution in the case of blast furnaces with large hearth diameters.
U.S. Pat. No. 3,693,812 issued Sept. 26, 1972 to R. Mahr et al discloses apparatus which permits the optimal uniform distribution of a furnace charge over the entire charging area. The novel charging apparatus of U.S. Pat. No. 3,693,812 comprises a distributing member rotatably arranged in the throat of a shaft furnace and angularly adjustable relative to the longitudinal axis of the furnace. The adjustable distributing member or chute is supplied from a centrally arranged spout; the spout providing communication between the distributing member and one or more storage hoppers in which charges of the furnace raw materials are temporarily stored. In the prior art such storage hoppers have conventionally been in the form of sluice bins which deliver materials to the centrally arranged spout via metering devices such as discharge channels, throttle members, vibration zones, etc.
The metering devices of the prior art have only served to prevent the direct unimpeded out-flow of the charge material to the distributing member. Thus, the main characteristic of previously known metering devices, in addition to exercising a degree of metering action by influencing the material flow rate, is a braking action which insures that too rapid a feed rate is avoided while simultaneously insuring that there will be an adequate feed rate to provide sufficiently large forces to prevent a blockage of the charge in the region of the supply hopper outlet port. The prior art metering devices have not been capable of accurately measuring the charge in the interest of facilitating control of the charging operation.